Ion source for calutrons



Sept. 16, 1958 J. R. ToLMlE 2,852,685

10N SOURCE FOR cALUTRoNs Filed Jan. 2e, 1945 s sheets-sheet 1 4 cc e/era /fng f/ec/fa de Sept- 16, 1958 l J. R. 'roLMlE 2,852,685

ION SOURCE FOR CALUTRONS Filed Jan. 26, 1945 5 Sheets-SheerI 2 Sept. 16, 1958 J. R. ToLMlE 2,852,635

ION SOURCE FOR CALUTRONS Filed Jan. 26, 1945 3 Sheets-Sheet 3 United States Patent C M' ION SOURCE FOR CALUTRONS John R. Tolmie, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application January 26, 1945, Serial No. 574,665

11 Claims. (Cl. Z50-41.9)

This invention relates to improvements in electric discharge devices, and more particularly to calutrons of the type disclosed in the copending application of Ernest O. Lawrence, Serial No. 557,784, tiled October 9, 1944, and issued May 24, 1955 as U. S. Patent No. 2,709,222.

A calutron is a device for increasing the proportion of a selected isotope in an element containing a plurality of isotopes in order to produce the element enriched with the selected isotope. Such a calutron essentially comprises means for vaporizing a quantity of material containing the element that is to be enriched with the selected isotope; means for subjecting the vapor to ionization, whereby at least a portion of the vapor is ionized, so that ions of the different isotopes are produced; electrical means for segregating the ions from the un-ionized vapor and for accelerating the segregated ions to relatively high velocities; magnetic means for deflecting the ions along curved paths, the radii of curvature of the paths of the ions being proportional to the square roots of the masses of the ions, whereby the ions are concentrated in accordance with their masses; and means for de-ionizing and collecting the ions of a selected isotope thus concentrated, thereby to produce a deposit of the element enriched with the selected isotope. The apparatus is especially useful in producing uranium enriched with U235.

One object of this invention is to provide a calutron ion source unit that is eicient in operation.

Another object of the invention is to provide a calutron ion source unit with cathode structure that is simple to manufacture, and that is sturdy and etlicient.

Another object of the invention is to provide a calutron ion source unit with an improved arrangement for utilizing a polyphase source of current for heating the cathode.

A further object of the invention is to provide a calutron ion source unit, an improved cathode in the form of a plate.

Further objects of the invention will appear to those skilled in the art from a reading of the following detailed description of apparatus embodying the invention.

Inthe accompanying drawings, forming part of the specication hereof,

Figure 1 is a diagrammatic plan view of a calutron including an ion source unit embodying the present invention;

Fig. 2 is a vertical sectional view of the calutron taken along the line 2-2 in Fig. l;

Pig. 3 is a vertical sectional view of the ion source unit incorporated in the calutron, taken along the line 3--3 in Fig. 7;

Fig. 4 is a front view of the ion source unit shown in Fig. 3;

Fig. 5 is an enlarged fragmentary view of the cathode structure -of the ion source unit, taken along the line 5-5 in Fig. 3; Y

Fig. 6 is a fragmentary plan View of the ion source unit; and

Fig. 7 is a horizontal sectional view of the ion source unit, taken along the line 7-7 in Fig. 3.

2,852,685 Patented Sept. 16, 1958 ICC - housed therein. The tank 13 is of tubular configuration,

being substantially arcuate in plan, and comprising substantially ilat parallel spaced-apart top and bottom walls 14 and 15, upstanding curved inner and outer side walls 16 and 17, and end Walls 18. and 19. The end walls 18 and 19 close the opposite ends of the tubular tank 13 and are adapted to be removably secured in place, whereby the tank 13 is hermetically sealed. Also, vacuum pumping apparatus 13a is associated with the tank 13, whereby the interior of the tank 13 may be evacuated to a pressure of the order 10-5 to 10*4 mm. Hg. Preferably, the component parts of the tank 13 are formed of steel, the top and bottom walls 14 and 15 thereof being spaced a short distance from the pole faces of the upper and lower pole pieces 11 and 12 respectively, the tank 13 being retained in such position in any suitable manner, whereby the top and bottom walls 14 and 15 constitute in effect pole pieces with respect to the interior of the tank 13, as explained more fully hereinafter.

The removable end wall 18 suitably supports an ion source unit 20 comprising a charge receptacle 21 and a communicating arc-block 22. An electric heater 23 is arranged in heat exchange relation with the charge receptacle 21 and is adapted to be connected to a suitable source of heater current supply, whereby the charge receptacle 21 may be appropriately heated, the charge receptacle 21 being formed of steel or the like. The arc-block 22 is formed, at least partially, of brass or the like and is substantially C-shaped in plan, an upstanding slot 24 being formed in the wall thereof remote from the charge receptacle 21. Thus, the arc-block 22 is of hollow construction, the cavity therein communicating with the interior of the charge receptacle 21.

Also, the removable end wall 18 carries a plate-shaped triangular cathode 25 the apices of which are connected to the terminals of the star connected secondary of the three phase transformer 36 forming the source of cathode current supply. The cathode 25 overhangs the upper end of the arc-block 22 and is arranged in alignment with respect to the upper end of the cavity formed therein. The arc-block 22 carries an anode 26 disposed adjacent the lower end thereof and arranged in alignment with respect to the cavity formed therein. Also, the arc-block 22 carries a collimating electrode 27 disposed adjacent the upper end thereof and having an elongated collimating slot 28 formed therethrough and arranged in alignment with respect to the cathode 25 as well as the anode 26 and the cavity formed in the arc-block 22. Both the anode 26 and the collimating electrode 27 are electrically connected to the source unit 20, which in turn is connected to the positive terminal of a suitable source of accelerating electrode potential supply, as explained more fully hereinafter. On the other hand, the tank 13 is grounded. Also, the cathode 25 and the cooperating anode 26 are adapted to be connected to a suitable source of arc current supply.

Further, the removable end wall 18 carries ion accelerating structure 29, formed at least partially of tungsten or the like, and disposed in spaced-apart relation with respect to the wall of the arc-block 22 in which the slot 24 is formed. More specifically, a slit 30 is formed in the ion accelerating structure 29 and arranged in substantial alignment with respect to the slot 24 formed in the wall of the arc-block 22. The source of accelerating electrode supply is adapted to be connected between the arc-block 22 and the ion accelerating structure 29, the positive and negative terminals of the supply mentioned being respectively connected to the arc-block 22 and to the ion accelerating structure 29. Further, the negative terminal of the ion accelerating electrode supply is grounded.

The removable end wall 19 suitably supports an collector block 31 formed of stainless steel or the like, and provided with two laterally spaced-apart cavities or pockets 32 and 33 which respectively communicate with aligned slots 34 and 3S formed in the Wall of the collector block 31 disposed remote from the removable end wall 19. lt is noted that the pockets 32 and 33 are adapted to receive two constituent isotopes of an element which have been separated in the calutron 1l), as eX- plained more fully hereinafter. Finally, the collector block 31 is electrically connected to the ion accelerating structure 29. Thus it Will be understood that the source unit is connected to the positive ungrounded terminal of the accelerating electrode supply; while the tank 13, the ion accelerating structure 29 and the collector block 31 are connected to the negative grounded terminal of the accelerating electrode supply; the source unit 26 being electrically insulated from the component parts of the tank 13. Thus the portion of the tank 13 disposed between the ion accelerating structure 29 and the collector block 31 constitutes an electrostatic shield for the high-velocity ions traversing the curved paths between the slit 30 formed in the ion accelerating structure 29 and the slots 34 and 35 formed in the collector block 31, as explained more fully hereinafter.

Considering now the general principle of operation of the calutron 10, a charge comprising a compound of the element to be treated is placed in the charge receptacle 21, the compound of the element mentioned being one which may be readily vaporized. rlhe end walls 18 and 19 are securely attached to the open ends of the tank 13, whereby the tank 13 is hermetically sealed. The various electrical connections are completed and operation of the vacuum pumping apparatus 13a associated with the tank 13 is initiated. When a pressure of the order of 105 to l0-4 mm. Hg is established within the tank 13, the electric circuits for the windings, not shown, associated with the pole pieces 11 and 12 are closed and adjusted, whereby a predetermined magnetic field is established therebetween traversing the tank 13. The electric circuit for the heater 23 is closed, whereby the charge in the charge receptacle 2l is heated and vaporized. The vapor tills the charge receptacle 21 and is conducted into the communicating cavity formed in the arc-block 22. The electric circuit for the cathode 25 is closed, whereby the cathode 25 is heated and rendered electron ernissive. Then the electric circuit between the cathode 2S and the anode 26 is closed, whereby an arc discharge is struck therebetween, electrons proceeding from the cathode 25 through the collimating slot 28 formed in the collimating electrode 27 to the anode 26. The collimating slot 2S formed in the collirnating electrode 27 defines the cross section of the stream of electrons proceeding into the arc-block 22, whereby the arc discharge has a ribbon-like configuration and breaks up the molecular form of the compound of the vapor to a considerable extent, producing positive ions 'of the element that is to be enriched with the selected one of its isotopes.

The electric circuit between the arc-block 22 and the ion accelerating structure 29 is completed, the ion accelerating structure 29 being at a high negative potential with respect to the arc-block 22, 'whereby the positive ions in the arc-block 22 are attracted by the ion accelerating structure 29 and accelerated through the voltage impressed therebetween. More particularly, the positive ions proceed from the cavity formed in the arc-block 22 through the slot 24 formed in the wall thereof, and across the space between the ion accelerating structure 29 and the adjacent wall of the arc-block 22, and thence through the slit 30 formed in the ion accelerating structure 29. The high-velocity positive ions form a vertical upstanding ribbon or beam proceeding from the cavity formed in the arc-block 22 through the slot 24 and the aligned slit 30.

As previously noted, the collector block 31, as well as the tank 13, is electrically connected to the ion accelerating structure 29, whereby there is an electric-tield-free path for the high-velocity positive ions disposed between the ion accelerating structure 29 and the collector block 31 within the tank 13. The high-velocity positive ions are deilected from their normal straight-line path and form a vertical plane passing through the slot 24 and the aligned slit 30, due to the etfect of the relatively strong magnetic ield maintained through the space within the tank 13 through which the positive ions travel, whereby the positive ions describe arcs, the radii of which are proportional to the square roots of the masses of the ions and consequently of the isotopes of the element mentioned. Thus, ions of the relatively light isotope of the elements describe an interior arc of relatively short radius and are focused through the slot 34 into the pocket 32 formed in the collector block 31; whereas ions of the relatively heavy isotope of the element describe an exterior arc of relatively long radius and are focused through the slot 35 into the pocket 33 formed in the collector block 31. Accordingly, the ions of the relatively light isotope of the element are collected in the pocket 32 and are de-ionized to produce a deposit of the relatively light isotope of the element therein; while the ions of the relatively heavy isotope of the element are collected in the pocket 33 and are de-ionized-to produce a deposit of the relatively heavy isotope of the element therein.

After all of the charge in the charge receptacle 21 has been vaporized, all of the electric circuits are interrupted and the end wall 18 is removed so that another charge may be placed in the charge receptacle 21 and subsequently vaporized in the manner explained above. After a suitable number of charges have been vaporized in order to obtain appropriate deposits of the isotope of the element in the pockets 32 and 33 of the collector block 31, the end wall 19 is removed and the deposits of the collected isotopes in the pockets 32 and 33 in the collector block 31 are reclaimed.

Of course, it will be understood that the various dimensions of the parts of the calutron 10, the various electrical potentials applied between the various electrical parts thereof, as well as the strength of the magnetic eld between the pole pieces 11 and 12, are suitably correlated with respect to one another, depending upon the mass numbers of the several isotopes of the element which is to be treated therein. In this connection reference is again made to the above noted patent of Ernest O. Lawrence, for a complete specification of a calutron especially designed for the production of uranium enriched with the isotope U235. By way of illustration, it is noted that when the calutron 10 is employed in order to produce uranium enriched with U235, the compound of uranium which is suggested as a suitable charge in the charge receptacle 21 is UC14, as this compound may be readily vaporized and the molecular form of the vapor may be readily broken up to form positive ions of uranium. In this case, uranium enriched with U235 is collected in the pocket 32 of the collector block 31, and uranium comprising principally U238 is collected in the pocket 33 of the collector block 31. Also, it is noted that from a practical standpoint, the deposit of uranium collected in the pocket 32 of the collector block 31 contains considerable amounts of Um, in view of the fact that this isotope comprises the dominant constituent of normal uranium. Furthermore, the deposit of uranium collected in the pocket' 32 of the collector block 31 contains a considerably increased amount of U234, in view of the fact that it is not ordinarily feasible to separate Um and U235 in the production of relatively large quantities of uranium enriched with U235 for commercial purposes. Accordingly, in this example the uranium deposited in the pocket 32 of the collector block 31 is considerably enriched, both with U234 and U235, and considerably impoverished with respect to U238 as compared to natural or normal uranium.

Referring now more particularly to Figs. 3 to 7, inclusive, of the drawing, there are illustrated the structural details of the ion source unit which is arranged in the magnetic eld between the pole pieces of the calutron in the manner previously explained, the source unit 20 com prising the charge receptacle 21 andthe arc-block 22. The charge receptacle 21 comprises wall structure, including a removable cover 50, defining an upstanding cavity 51 therein, that is adapted to receive a removable charge bottle 52 containing a charge 53 to be vaporized. The

arc-b1ock 22 comprises wall structure defining an up? standing distributing chamber 54 and an upstanding arc chamber 55 therein, the cavity 51 communicating with the distributing chamber 54 through a tubular member 56 supported by the wall structure of the charge receptacle 21 and the wall structure of the arc-block 22. The rear wall structure of the charge receptacle 21 has two upstanding cavities 57 formed therein, in which two elements of the electric heater 23 are arranged. Preferably, each element of the electric heater 23 comprises a coil of resistance wire wound on a supporting insulator, as indicated, whereby each element of the electric heater 23 may be independently placed in and removed from the associated cavity 57. Thus, the charge receptacle 21, and consequently the charge bottle 52, may be appropriately heated in order to vaporize the charge 53 contained in the charge bottle 52. Similarly, the arc-block 22 has two upstanding cavities 58 formed therein, in which two electric heating elements 59 are arranged. Preferably, each of the electric heating elements 59 comprises a coil of resistance wire wound on a supporting insulator, as indicated, whereby each of the electric heating elements 59 may be independently placed in and removed from the associated cavity 58. Thus, the arc-block 22, and more particularly the distributing chamber 54 therein, may be heated in order to prevent condensation of the contained vapor, as explained more fully hereinafter.

More particularly, the ywall structure of the charge receptacle 21 is formed of copper or brass; and the wall structure of the arc-block 22 is formed of copper or brass and comprises two primary members 60 and 61. The distributing chamber 54 and the cavities 58 `are formed in the member 60; while the arc chamber 55 is formed in the member 61, a series of longitudinally spaced-apart openings 62 being formed in the wall of the member 61 and communicating ybetween .the distributing chamber 54 and the arc chamber 55. Also, the arc-block 22 comprises front plates 63 formed of copper or brass fand secured to the member 61; the source unit 20 'being sup- -ported by two rearwardly extending arms y64 which are secured to the `member 61 and the front plates 63.

Two upstanding lstrips 65, formed of tungsten or the like, are secured to the member 61 adjacent the arc chamber 55, there-by to dene an upstanding slot therebetween communicating with the arc chamber 55. Also, two upstanding strips 66, formed of tungsten or the like, are secured one to each of the front plates 63 adjacent the strips 65 and spaced a small distance forwardly with respect thereto, thereby to dene an upstanding slot between the strips 66 communicating with the arc chamber 55. Thus, the `slot defined between the strips 65 and the slot defined between the vstrips 66 constitute the upstanding slot 24 formed `in the front wall of the arc-block 22 and communicating with the arc chamber 55.

The triangular cathode is supported substantially at its apices by cathode structure 67 arranged in cooperating relation with respect to the arc-block 22. The cathode 25 overhangs the collimating electrode portion 27 of the top wall of the arc-block 22, the collimating electrode 27 being secured to the top wall of the arc-block 22 and having the transverse slot 28 formed therein communicating with the arc chamber 55. More particularly, the cathode 25 is spaced fa short distance above the collimatin'g electrode 27, the central portion of the front side of the triangular cathode 25 being arranged in alignment with the transverse slot 28 formed in the collimatin'g electrode 27- Also, the anode 26 is secured to the bottom of the arc-block 22 and forms the bottom wall of the ar-c chamber 55, this anode 26 being in alignment with the central portion of the front side of the triangular cathode 25 and the 'transverse slot 28 formed in the collimating electrode 27.

The negative and positive terminals of the arc supply are respectively connected to the cathode 25 and to the arc-block 22, the anode 26 and the collimating electrode 27 'being connected together -by the arc-block 22 and consequently to the positive terminal of the arc `supply rnen-A tioned, as previously noted.

Further, the ion accelerating structure 29 comprises, two upstanding strips `69 disposed forwardly of the strips 66 and secured to two transversely-extending top and bottom members 70 and 71 respectively to form a unitary structure. The two strips 69 are arranged in transverse spaced-apart relation and carry two electrodes 72, formed of tungsten or the like. The two electrodes 72 are arranged in transverse spaced-apart relation to dene the upstanding slit 30 therebetween, and arranged in alignnient with the slot 24 formed in the front wall of the arc-block 22.

As previously noted, the ion accelerating structure 29, together with the source unit 2t), is supported 'by the removable end wall 18 of the calutron l0, and the posi-A tive and negative terminals of the accelerating electrode supply are respectively connected to the arc-block 22 and the ion accelerating structure 29. Finally, an upstanding semicircular baile plate 73, formed of quartz or the like, is arranged in the arc chamber 55, and has a series of longitudinally spaced-apart openings 74 formed therein.

With particular reference to the cathode 25, it will be noted that this element is in the form of a triangular plate having three projecting rectangular apices 76, 77, and 78. The cathode 25 is so positioned that it overhangs and is perpendicular to the longitudinal axis of the arc chamber 55, with the object of producing a copious and uniform flow of electrons into the arc chamber 55. The apices 76, 77, and 78 are removably clamped to respective terminals 79, 80, Iand 81 by 4means of clamping screws 82 or the like whereby the cathode 25 is replaceable. The terminal 79 is integral with a rigid conductor 83. The other two terminals and 8l are provided lwith angular upstanding portions `84 and 85, respectively, that are slotted to permit clamping about two circular rigid conductors 86 and 87, respectively, with the aid of clamping screws 88. The conductors 83, '86, and 87 are all carried by the supporting member 67, and are connected to the respective wires 37, 38, and 39.

The electrical energy for the cathode 25 is supplied by the polyphase transformer 36. The legs of the star or Y-connected secondary of the transformer 36 are suitably connected with the wires 37, 38, and 39 to the apices of the cathode 25 whereby energizing t-he primary .of the transformer will cause polyphase current to flow in the cathode 25. The secondary of the transformer 36 is Y-connected, and the neutral thereof is joined to the negative terminal of the arc supply.

The cathode 25 embodied in the present invention has 'been found to 'be very sturdy and to be uniformly emi-ssive over a considerable area. While the cathode 25 in the preferred form is shown in the shape of a triangle, it is understood that it may be square, rectangular, pentagonal, or, indeed, have any number of Isides more than two. If desired, as many phases of current may 'be used to energize the plate as there are sides, althoughiit is 7 obvious, of course, that three phase current may be used with a plate cathode `having more than three sides. The cathode 25 maybe made of tungsten or tantalum, and, lby virtue of the rigid conductors $3, 36, and 37, is carried by the supporting member 67.

Considering now the detailed operation of the ion source unit 2l), when the electric circuit for the heater 23 is completed the charge receptacle 21 and consequently the charge bottle 52 are heated, whereby the charge 53 is vaporized, filling the cavity in t'ne charge bottle 52. The vapor passes through the tubular member 56 into the distributing chamber 54, whereby this chamber is lled with the vapor. The vapor is distributed in the distributing chamber 54 and passes through the openings 62 formed in the wall of the member 61 into the rear part of the arc chamber 55. The vapor then passes through the openings 74 formed in the baie plate 73, into the front part of the arcv chamber 55, whereby this part of the arc chamber 55 is filled with the vapor. More particularly, the arc chamber 55 is thoroughly and substantially uniformly lled with the vapor to be ionized, due to the arrangement of the distributing chamber 54 and the bafe plate 73.

When the circuit for the cathode 25 is completed, the cathode is heated and rendered electron emissive; and when the arc supply circuit is completed between the cathode 25 and the arc-block 22, electrons are projected from `the central portion of the cathode 25 toward the collimating electrode 27. More particularly, some of these electrons pass through the transverse slot 28 formed in the collimating electrode 27, into the arc chamber 55, and proceed toward the anode 26. Accordingly, the collimating electrode 27 causes a stream of electrons having a ribbon-like configuration to be projected through the are chamber 5S, whereby the vapor in the arc chamber is ionized. When the accelerating electrode supply circuit is completed, the positive ions produced in the arc chamber 55 are drawn through the upstanding slot 24 formed in the front wall of the arc-block 22 by the associated ion accelerating structure 29, to form a beam of positive ions having an upstanding substantially ribbonlike configuration proceeding through the slit 30 between the electrodes 72; which beam of positive ions is projected through the evacuated tank space toward the cooperating collector block 31, in the manner previously explained.

In View of the foregoing description, it will be understood that the calutron comprises an ion source unit 20 including a single ion transmitter arranged to transmit a single beam of ions through the evacuated tank space in the tank 13 to the ion collector block 31, the collector block 31 constituting an ion receiver. Hence, the calutron 10 comprises a single transmitter arranged to transmit a single ion beam to a single receiver, the transmitter being supported by the removable end wall 18, and the receiver being supported by the removable end wall 19 of the tank 13, as previously explained.

What is claimed is:

1. In an ion source for a calutron, a substantially triangular plate-like cathode, and means including a polyphase source of heating current connected to said cathode at the apices thereby rendering it electron emissive.

2. In an ion source for a calutron, a plate-like cathode having the general coniiguration of a polygon including a given number of apices, and polyphase source of current having a phase connected to each of said apices for rendering said cathode electron emissive.

3. A calutron ion source, comprising wall structure defining a chamber adapted to contain gas to be ionized, a plate-shaped cathode adapted to discharge electrons into said chamber, and a polyphase source of current connected to substantially equi-spaced points on said cathode at a maximum distance from the center of said cathode.

4. A calutron ion source, comprising wall structure deiining a chamber adapted to contain gas to be ionized, a triangular` plate cathode adapted to discharge electrons into said gas chambenand a three-phase source .of current operatively connected to the apices of said cathode.

5. In :a .calutron, an ion source comprising a triangular lplate cathode, three conductors, and three terminals connecting said conductors to the respective ones of the three apices of said cathode, at least one of said terminals being bent at an angle so that its associated conductor does not lie in the plane of said cathode.

6. In a calutron, an ion source comprising wall structure defining an are chamber, a plate-shaped electron emissive cathode adapted to discharge electrons into said chamber, a source of polyphase current, and means connecting said source to spaced-apart terminals of said cathode whereby a polyphase current flows in the cathode.

7. In a calutron ion source, a triangular plate-shaped cathode having a plurality of terminals integral therewith projecting substantially from the apices thereof, and a star-connected polyphase source of current supply connected to said terminalsv whereby the heating current'to each of the sides of said'triangular plate-shaped cathode is furnished by atleast Atwo phases of said polyphase source of current supply.

8. In a calutron .ion source, apolygonal plate-shaped cathode having a plurality of terminals integral therewith projecting substantially from the apices thereof, and a polyphase source of current supply connected to said terminals such that the heating current to the sides of said polygonal plate-shaped cathode is furnished by at least two phases of said polyphase source of current supply.

9. A calutron ion source comprising wall structure defining an elongated are chamber, an anode at one end of said arc chamber, a -collimating electrode having an elongated slot extending at least partially across said arc chamber positioned at the other end of said arc chamber, means for feeding gas to be ionized to said arc charnber substantially uniformly throughout the length of said chamber, Va plate-shaped cathode positioned to overhang the slot of said collimating electrode, a source of polyphase current connected to said plate-shaped cathode for heating said cathode, said connections being made to substantially equi-spacedA points on said cathode at a maximum distance Afrom the center thereof, and a source of current supply connected between said cathode, said collimating electrode `and said anode for producing a ribbon-like stream of electrons from said plate-shaped cathode through the slot of said collimating electrode into said arc chamber for ionizing said gas.

l0. A calutron ion source comprising wall structure defining an elongated arc chamber, an anode at one end of said arc chamber, a collimating electrode having7 an l elongated slot extending at least partially across said arc chamber positioned at the other end of said arc chamber, means for feeding gas to be ionized to said arc chamber substantially uniformly throughout the length of said chamber, a polygonal plate-shaped cathode positioned to over-hang the slot of said collimating electrode, a polyphase source of alternating current having the dilferent phases thereof connected to dilferent apices of said polygonal plate-shaped cathode for heating said cathode, and a source of current supply connected between said cathode, said collimating electrode and said anode for producing a ribbon-like stream of electrons from said plate-shaped cathode through the slot of said collimating electrode into said are chamber for ionizing said gas.

ll. A calutron ion source comprising wall structure dening an elongated arc chamber, a collimating electrode having a slot positioned transversely of said arc chamber at one end thereof, a polygonal plate-shaped cathode positioned over the slot of said collimating electrode so that a substantially uniformly electron emissive area of the surface of said cathode extends well over `said slot, a source of polyphase alternating current having the different phases thereof connected to dilferent apices of said polygonal plate-shaped cathode for heating said cathode, means for feeding gas to be ionized to said arc chamber substantially uniformly throughout the length of said chamber, and a source of current supply connected between said cathode and said collimating electrode for projecting a ribbon-like stream of electrons from said cathode into said are chamber through said slot to ionize the gas in said chamber.

1,771,704 Bethenod July 29, 1930 10 Romhild Dec. 6, 1932 Gurtler Apr. 10, 1934 Davisson May 17, 1938 Lawlor Aug. l5, 1944 Hoskins Apr. 24, 1945 FOREIGN PATENTS Great Britain Oct. 16, 1936 Great Britain Aug. 1, 1940 

